1. Field of the Invention
This invention relates to drug containing matrices for use in transdermal drug delivery devices. In another aspect this invention relates to pressure sensitive skin adhesives. In yet another aspect this invention relates to pharmaceutical formulations involving a pressure sensitive skin adhesive layer.
2. Description of the Related Art
Transdermal drug delivery devices are designed to deliver a therapeutically effective amount of drug across the skin of a patient. Devices known to the art include reservoir type devices involving membranes that control the rate of drug release to the skin and devices involving a dispersion of the drug in a matrix. Certain acrylic copolymers have been used as matrices for delivery of specific drugs. It is critical in such devices that intimate skin contact be achieved and maintained between the skin and the drug-containing matrix. Thus the range of copolymers that are suitable for use as matrices is limited by the ability of the copolymer to comply to the surface of the skin and still release cleanly from the skin. Moreover, the skin presents a substantial barrier to ingress of foreign substances such as drugs into the body. It is therefore often desirable or necessary to incorporate certain materials that enhance the rate at which the drug passes through the skin.
Certain transdermal drug delivery devices have incorporated pressure sensitive adhesive (“PSA”) matrices. Fundamentally, PSA's require a balance of viscous and elastic properties which result in a four-fold balance of adhesion, cohesion, stretchiness, and elasticity. In essence, PSA products have sufficient cohesiveness and elasticity so that, despite their tackiness, they can be handled with the fingers and removed from the skin without leaving substantial residue.